Module grounding analysis-600V residential [RE-wrenches]
William Miller
wrmiller at charter.net
Tue May 22 00:07:21 PDT 2007
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I am resending the post below because Topica apparently ate my first attempt:
Friends:
I read the article, suggested on this forum, analyzing grounding
problems. The article was written by Thomas Bowes. Here is a more
manageable link to the article:
http://tinyurl.com/yo3ckx
I found the article to be very germane to safety issues emerging as
industry installation practices evolve. The most important point made, in
my opinion, is the point that installation of 600 volt systems in
residential settings is a very new concept. This idea has implications
beyond just the grounding issues.
I have some very strong safety concerns prompted by this knowledge. What
causes me dismay is that the industry is hell-bent on cheapening and
speeding up installation techniques. I believe the motivation is partly to
make Utility-interconnected PV systems more accessible to the masses, which
is a good motivation. The other motivation is to obtain an advantage over
competing vendors of systems, a bad thing.
It is, in my opinion, not a matter of if, but when we kill our first human
(if it has no happened already) with our shoddy installation
procedures. My scariest scenario is of the child who throws a Frisbee or
ball onto a roof to have it become stuck under a PV array. A USE cable has
been rubbing against abrasive roofing material, exposing the
conductor. The child finds a length of metallic pipe in the garage and
uses it to dislodge the toy. You imagine the rest of the story...
The trend in reducing wire protection is driven also in part by practices
in Europe. It is my understanding that the "quick-connect" is ubiquitous
there and that leads from the roof to the inverter and from the inverter to
the AC distribution are all USE or similar cable, not protected by
conduit. Does anyone have experience with these European standards or
practices?
Lastly, the point made in the article is very correct in that if a module
in a "top-down" installation has a short circuit, how does one remove the
module without getting electrocuted? This is particularly risky when one
can not verify the short circuited module until one removes it from the
ground connection and undergoes a very real risk of becoming the ground
path, with possible fatal consequences.
I'd like to hear from those that share my concerns about these
practices. I would hope we could, as a group, put aside our pursuit of
paying contracts long enough to convene an installer based group to examine
some of these concerns.
William Miller
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